Solvent cleaners are known for their excellent cleaning ability, quick drying, metal compatibility, and low surface tension to facilitate penetration. Some solvents are known for the air pollution they cause (as volatile organic compounds or VOC), toxicity, flammability, and incompatibility with plastics. The use of volatile organic compounds (VOC) solvents has been discouraged due to their deleterious effect on the environment. Regulations have been promulgated to accelerate the phase-out of environmentally destructive solvents.
The Environmental Protection Agency (“EPA”) promulgates rules and regulations regarding environmental concerns such as VOCs. EPA has defined VOC's to include volatile compounds of carbon which promote atmospheric photo-chemical reactivity. Thus, there is a need to reduce the use of conventional VOC solvents and it is apparent that there is a need for solvents which have little or no VOC content.
The old specification solvent, commonly called Stoddard solvent or mineral spirits, contain petroleum fractions that are complex mixtures of aliphatic hydrocarbons, but may contain some aromatics and olefinics. P-D-680 contains hazardous air pollutants (HAP's) and VOC's and causes health and environmental concerns. The revision to MIL-PRF-680 eliminated the HAP's but MIL-PRF-680 still covers a petroleum-based solvent containing the same amount of VOC's as P-D-680. Since P-D-680 was first written, these solvents have been specified for general cleaning to remove oil and grease from aircraft and engine components and from ground support equipment.
The purpose of this invention is to develop a non-aqueous, low-volatile organic compound (VOC) containing and hazardous air pollutant—(HAP) free cleaner to meet the new environmental regulation in California (Rule 1171). VOCs are released during cleaning operations, contributing to the formation of ground-level ozone (photochemical smog), which can damage lung tissue, cause respiratory illness, and damage vegetation. Solvent emissions are regulated regionally and locally, with the air pollution control districts in California implementing the most stringent requirements. The South Coast Air Quality Management District (SCAQMD) has recently imposed restrictions limiting the VOC content in solvents to no greater than 25 grams per liter for immersion cleaning processes unless the solvent is used in an airtight cleaning system. In addition, under Title III of the 1990 Clean Air Act (CAA) amendment, the U.S. Environmental Protection Agency (EPA) established emissions standards for categories and sub-categories of sources that emit or have the potential to emit listed HAPs.
Wipe solvents are essential for removing contaminants from parts and surfaces before it undergoes manufacturing operations that require clean surfaces, such as painting, sealing, bonding, welding, plating, and other applications. High VOC-containing, high vapor pressure solvents are currently utilized for cleaning aircraft exteriors and parts applications. Currently, most of the products used by the Fleet Readiness Centers (FRCs) for wipe-cleaning applications contain HAPs high VOC contents of greater than 700 g/l. VOCs are released during cleaning operations, contributing to the formation of ground-level ozone (photochemical smog) and causing environmental and health problems. Furthermore, paint thinners, which contain HAP mixtures, are also used for general-purpose hand wipe-cleaning operations as specified in maintenance and corrosion control manuals. Continuing with the use of paint thinners as pre-paint cleaning solvents increases the risk of non-compliance and subsequent fines. Currently, the Navy's NAVAIR 01-1A-509 Cleaning and Corrosion Control manual lists three specifications for wipe-solvent cleaning applications:                1. MIL-T-81772 (Thinner, Aircraft Coating) covers the requirements for three types of thinner to be used in reducing aircraft coatings.        2. AMS 3166 (Solvent Cleaning Prior to Application of Sealing Compounds) is used to clean aircraft primary and secondary structural surfaces prior to application of adhesion promoters and/or sealing materials.        3. ASTM D329 (Acetone) is used for general-purpose hand-wipe cleaning operations. Acetone is an exempt solvent and it is very flammable and it is not compatible with plastics.        
The AMS 3166 specification is a Commercial Item Description (CID) and contains only one approved product (Dysol's DS-108). The VOC contents of the DS-108 product is more than 800 g/l and its vapor pressure is as low as 1.1 mmHg. According to NESHAP requirements, the vapor pressure for the wipe solvent cleaners should be around 45 mmHg. None of the MIL-T-81772 qualified products comply with the current environmental regulations (EPA and the SCAQMD). The Material Safety Data Sheet (MSDS) for Acetone (ASTM D329) has shown that Acetone is toxic to central nervous system (CNS). Also, it may be toxic to kidneys, the reproductive system, liver and skin. Repeated or prolonged exposure to Acetone can produce target organ damage. Due to the lack of environmentally-friendly qualified products, the FRCs are using hazardous cleaners such as Desoclean 45 for general-purpose hand-wipe cleaning applications on the F/A-18 aircraft. Because of various EPA Clean Air Act amendments and Resource and Conservation Recovery Act (RCRA) emission restrictions for HAPS/VOC's, along with California's more stringent SCAQMD VOC restrictions, solvents utilized at some aviation facilities cannot be applied for general-purpose wipe-cleaning operations.
Compositions of the linear or open-chain siloxanes of this invention (Wipe Solvent Formulations) are as follows:
EXAMPLE 1Parts By WeightHexamethyldisiloxane55 to 75Octamethyltrisiloxane25 to 45
EXAMPLE 2Hexamethyldisiloxane60 to 70Octamethyltrisiloxane30 to 40
Example 3Hexamethyldisiloxane62 to 65Octamethyltrisiloxane35 to 38
Example 4Hexamethyldisiloxane63 (63%)Octamethyltrisiloxane37 (37%)Properties of the NAVWIPE (Wipe Solvent Formulation)
Several commercial exempt solvents were selected for testing and evaluation for wipe cleaning applications in accordance with the requirements of MIL-PRF-32295A Type III (Table 1). Drying times after cleaning with solvents play an important role in industrial cleaning applications. The drying process depends on several factors such as the vapor pressure of the cleaning solvent, temperature, humidity, and the velocity of the airflow. The Aerospace National Emission Standards for Hazardous Air pollutants (NESHAP) (40 CFR 63 Subpart GG) limits the vapor pressure values for wipe cleaning applications to equal or less than 45 mmHg at 20° C. The vapor pressure of this invention (Navwipe) was determined to be about 31 mmHg at 20° C. as shown in Table 1. Few of the selected commercial products have met NESHAP's vapor pressure requirements for wipe-cleaning applications.
TABLE 1Comparison of Navwipe with Selected CommercialSolvent Products for Wipe-Cleaning ApplicationsVapor PressureManufacturerProductVOCmmHg at 20° C.DuPontVertrel XFExempt226GarrettHigh Sol-XExemptNAServices, Inc.PPGEsol-146ExemptNAaerospacePRC-DeSotoMicro CareSilicon Carrier FluidExempt226Sigma-AldrichAcetoneExempt184LyondellTer-Butyl AcetateExempt42NAVAIR(Navwipe)Exempt31InventionAGCAshiklin AE 3000Exempt233ChemicalsAmericaAGCAshiklin AE 3100EExempt210ChemicalsAmericaKowaDimethyl CarbonateExempt55AmericanCorp.Effect on Plastics (Crazing Test)
The effect of the siloxane composition and selected commercial products on plastics was studied in accordance with ASTM F 484. The plastic materials used for this test are listed below:                a. MIL-PRF-5425 cast acrylic (annealed in accordance with ASTM F 484)        b. MIL-PRF-25690 stretch acrylic        c. SAE AMS-P-83310 polycarbonate        
The specimens were secured in the loading fixture. The product was applied onto the top surface of the plastic by spraying back and forth three times in ten seconds from a distance of six inches. The test coupons were allowed to air dry for one hour and then were examined for crazing and strength loss. Crazing is evident when a flashlight is used to illuminate the specimen from a direction tangent to the specimen bend. Strength loss is evident if, when removed from the fixture, it fails easily when bent by hand. The results of the crazing test for the selected commercial products and the new invention on the cast acrylic plastic are shown in Table 2. All tested products failed the crazing test with the exception of the siloxane composition of this invention, (Navwipe) which met the requirement. In addition, the siloxane composition (Navwipe) passed the test requirements of stretch acrylic and polycarbonate materials.
TABLE 2Compatibility of Selected Commercial Productson Plastics (Crazing Test: ASTM F 484)Cast AcrylicProductMIL-PRF-5425High Sol-XFailEsol 146FailDimethyl CarbonateFailAcetoneFailAshiklin 3100EFailAshiklin 3000FailTer-Butyl AcetateFailNavwipePASS
The cleaning efficiency test for Navwipe cleaner was conducted in accordance with test method 4.5.9 in MIL-PRF-32295A Type III as described below.
Preparation of test specimens: Stainless steel coupons of 1 by 2 by 0.05 inches (25 by 50 by 1.3 mm) were polished with 240-grit aluminum oxide abrasive paper or cloth and solvent wiped with isopropyl alcohol. Coupons were weighed (weight=W1), coated on one side with 20-25 mg of soil, then reweighed (weight=W2). Soils used for testing were the following:                a. MIL-G-21164 (Grease, Molybdenum Disulfide, for Low and High Temperatures)        b. MIL-PRF-83282 (Hydraulic Fluid, Fire Resistant, Synthetic Hydrocarbon Base)        c. MIL-PRF-10924 (Grease, Automotive and Artillery)        
Test Procedure.
Fresh solvent was used for each soil tested. Each test coupon was cyclically immersed and withdrawn from a 150-ml beaker containing 100 ml of the cleaner at a rate of 20 cycles per minute for 5 minutes. Each coupon dried for 10 minutes at 140±4° F. (60±2° C.), cooled to room temperature, and reweighed (weight=W3). Cleaning efficiency for the cleaner was calculated as follows for each coupon:% Cleaning Efficiency=(W2−W3)/(W2−W1)×100
The cleaning efficiency of the siloxane composition (Navwipe) was conducted in accordance with the requirements of MIL-PRF-32295A Type III and the results are shown in Table 3. In addition, the results of cleaning efficiency of the selected products on one soil (MIL-G-21164) are shown in Table 4. As shown in FIG. 1, the results indicate that the siloxane compositions of this invention (Navwipe) is the only product that meets the requirements of MIL-PRF-32295A Type III.
TABLE 3Cleaning Efficiency Test Results fora. Siloxane Composition (Navwipe)ProductMIL-PRF-32295A Type IIINew InventionSoilRequirements(Navwipe)MIL-G-2116470%71%MIL-PRF-1092485%96%MIL-PRF-8328295%97%
TABLE 4Cleaning Efficiency Test Results for the SelectedCommercial Products in Accordance with MIL-PRF-32295A Type III (MIL-G-21164 Soil)Cleaning EfficiencyPercentage (%)Product(MIL-G-21164 Soil)Vertrel-XF62.1High Sol-X67.0Esol 14668.8Silicon Carrier Fluid67.0LHB66.95Methyl Acetate66.97Dimethyl Carbonate64.70Ashiklin AE-3100E65.40Ashiklin AE-300060.40Solkane 365 mfc63.95Acetone64.80Siloxanes (Navwipe)71.00
The specific siloxanes of this invention consist essentially of linear or open-chain alternating silicon and oxygen atoms wherein the prefix denotes the number of silicon atoms alkylated with methyl groups. It was found that the di and trisiloxane mixtures alkylated with alkyl methyl groups (Navwipe) were the only products that met the requirements of MIL-PRF-32295A Type III as shown by the data in Table 3 and FIG. 1.
The benefits of the siloxane compositions of this invention are providing the fleet with effective, safe, environmentally-friendly wipe-solvent cleaner. Providing qualified cleaners to all levels of maintenance will avoid risk of use of improper materials, which may compromise performance, safety and health. In addition, the outcomes of this invention are improving the fleet readiness, and pollution prevention onboard ships and complying with the current environmental regulations. To meet the new environmental regulations, it is essential to identify and validate effective, safe, and environmentally friendly products for cleaning applications. The Navwipe will be used to clean weapon systems across Department of Defense (DOD) maintenance facilities as alternatives to the current high VOC products. The advantages of the Navwipe cleaner include:                Exempt Solvent,        Odorless properties,        Free of HAPs,        Compatible with metals and non-metals,        Non-toxic,        Dry fast,        Contains no ozone-depleting substances (ODSs),        Cleaning efficiency is equivalent to the high VOC control,        Complies with EPA and the new environmental regulations,        A new alternative for high VOC commercial products, and        Provides a safer and environmentally friendly cleaner to the fleet.        
The siloxane composition (Navwipe) will be used for cleaning aircraft structure (metal and composite) surfaces prior to painting, sealing, bonding, application of adhesion promoters. In addition, the Navwipe will be used as a replacement for hazardous chemicals currently used by the fleet such as methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK), and MIL-T-81772 for wipe-cleaning applications.
While various embodiments of the invention have been disclosed, the specific composition and methods described herein are not intended to limit the scope of the invention.